Update according to review comments iluwatar#397

- Added descriptions
- Added junit tests
- Added javadoc
- Added index.md
- Added class diagrams

Author: gwildor28

mutex/etc/mutex.png

@@ -0,0 +1,30 @@
+---
+layout: pattern
+title: Mutex
+folder: mutex
+permalink: /patterns/mutex/
+categories: Lock
+tags: 
+ - Java
+ - Difficulty-Beginner
+---
+
+## Also known as
+Mutual Exclusion Lock
+Binary Semaphore
+
+## Intent
+Create a lock which only allows a single thread to access a resource at any one instant.
+
+![alt text](./etc/mutex.png "Mutex")
+
+## Applicability
+Use a Mutex when
+
+* you need to prevent two threads accessing a critical section at the same time
+* concurrent access to a resource could lead to a race condition 
+
+## Credits
+
+* [Lock (computer science)] (http://en.wikipedia.org/wiki/Lock_(computer_science))
+* [Semaphores] (http://tutorials.jenkov.com/java-concurrency/semaphores.html)

mutex/index.md

@@ -2,7 +2,7 @@
 <!--
 
     The MIT License
-    Copyright (c) 2014 Ilkka Seppälä
+    Copyright (c) 2014 Ilkka Sepp�l�
 
     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal
@@ -32,4 +32,11 @@
     <version>1.11.0-SNAPSHOT</version>
   </parent>
   <artifactId>mutex</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency> 
+  </dependencies>
 </project>

mutex/pom.xml

@@ -23,7 +23,15 @@
 package com.iluwatar.mutex;
 
 /**
- * App.
+ * A Mutex prevents multiple threads from accessing a resource simultaneously.
+ * <p>
+ * In this example we have two thieves who are taking beans from a jar.
+ * Only one thief can take a bean at a time. This is ensured by a Mutex lock
+ * which must be acquired in order to access the jar. Each thief attempts to
+ * acquire the lock, take a bean and then release the lock. If the lock has 
+ * already been acquired, the thief will be prevented from continuing (blocked)
+ * until the lock has been released. The thieves stop taking beans once there
+ * are no beans left to take.
  */
 public class App {
 

mutex/src/main/java/com/iluwatar/mutex/App.java

@@ -23,20 +23,28 @@
 package com.iluwatar.mutex;
 
 /**
- * Jar.
+ * A Jar has a resource of beans which can only be accessed by a single Thief
+ * (thread) at any one time. A Mutex lock is used to prevent more than one Thief
+ * taking a bean simultaneously. 
  */
 public class Jar {
 
-  private Lock lock;
+  /**
+   * The lock which must be acquired to access the beans resource.
+   */
+  private final Lock lock;
 
+  /**
+   * The resource within the jar.
+   */
   private int beans = 1000;
 
   public Jar(Lock lock) {
     this.lock = lock;
   }
 
   /**
-   * takeBean method
+   * Method for a thief to take a bean.
    */
   public boolean takeBean(Thief thief) {
     boolean success = false;

mutex/src/main/java/com/iluwatar/mutex/Jar.java

@@ -23,7 +23,7 @@
 package com.iluwatar.mutex;
 
 /**
- * Lock.
+ * Lock is an interface for a lock which can be acquired and released.
  */
 public interface Lock {
 

mutex/src/main/java/com/iluwatar/mutex/Lock.java

@@ -23,11 +23,20 @@
 package com.iluwatar.mutex;
 
 /**
- * Mutex.
+ * Mutex is an implementation of a mutual exclusion lock.
  */
 public class Mutex implements Lock {
-  private Object owner = null;
 
+  /**
+   * The current owner of the lock.
+   */
+  private Object owner;
+
+  /**
+   * Method called by a thread to acquire the lock. If the lock has already
+   * been acquired this will wait until the lock has been released to 
+   * re-attempt the acquire.
+   */
   @Override
   public synchronized void acquire() throws InterruptedException {
     while (owner != null) {
@@ -37,6 +46,9 @@ public synchronized void acquire() throws InterruptedException {
     owner = Thread.currentThread();
   }
 
+  /**
+   * Method called by a thread to release the lock.
+   */
   @Override
   public synchronized void release() {
     owner = null;

mutex/src/main/java/com/iluwatar/mutex/Mutex.java

@@ -23,19 +23,30 @@
 package com.iluwatar.mutex;
 
 /**
- * Thief.
+ * Thief is a class which continually tries to acquire a jar and take a bean
+ * from it. When the jar is empty the thief stops.
  */
 public class Thief extends Thread {
 
-  private String name;
-
-  private Jar jar;
+  /**
+   * The name of the thief. 
+   */
+  private final String name;
+  
+  /**
+   * The jar
+   */
+  private final Jar jar;
 
   public Thief(String name, Jar jar) {
     this.name = name;
     this.jar = jar;
   }
 
+  /**
+   * In the run method the thief repeatedly tries to take a bean until none
+   * are left.
+   */
   @Override
   public void run() {
     int beans = 0;

mutex/src/main/java/com/iluwatar/mutex/Thief.java

@@ -0,0 +1,34 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.mutex;
+
+import org.junit.Test;
+import java.io.IOException;
+
+public class AppTest{
+  @Test
+  public void test() throws IOException {
+    String[] args = {};
+    App.main(args);
+  }
+}